This invention relates to a case structure for rotary machines having a prevailing axial extension. The invention is specially useful in the manufacture of electric motors and of pumps, particularly multi-stage pumps.
According to prior art techniques, cylindrical configuration rotary machines having a prevailingly axial extension (such as electric motors, and pumps) are produced by assembling the various electrical and mechanical components within cylindrical casings, in general of cast metal.
Such casings, in the instance of an electric motor, contain, by force fit or fastening through dowels or screws, the stator portion, whereas the rotor portion is carried by end caps which are centered and secured to the casing by means of screws, studs or through tie bolts.
The expert will recognize that the accomplishment of a structure so conceived involves the availability of an outer case, to be produced either by casing or machining a cylindrical body, and machining and finishing steps for providing it with detent, centering and securing devices for the parts contained therein.
When insertion of the inner components is carried out by force fitting under a press, then it will be apparent that subsequent disassembly for servicing purposes is a difficult process, as not easy is replacement of the stator windings unless the stator assembly is a removable one.
In addition to the above, if the machine has a considerable axial extension, as is the case with multi-stage pumps and motors where constraints to a limited diameter result in an increase of axial length, assembling of the end caps by means of tie rods and bars of considerable length further involves centering and alignment problems.
In an attempt to attenuate such problems, cases have been given an increased thickness dimension, and machined abutments have been formed thereon for centering the end caps, or alternatively threads for threadably engaging the same.
No less important than the technical problems mentioned above, are those problems which are connected with manufacturing economy, such as the time for preparing and machining the various components, in addition to the assembling time therefor, which are of considerable import indeed and affect the final cost of the resulting product in a decisive manner.
A similar situation is encountered by servicing, where disassembly and reassembly of the various parts are far from convenient to carry out, and involve much time and qualified labor.
In the instance of motors having a very long stator assembly, and small diameters, rewinding is virtually impossible unless the stator is removed from the case.